The statements in this section merely provide background information related to the present disclosure and do not constitute prior art.
In order to meet recently increasing data traffic, capacity expansion of existing optical communication networks is developed.
For this reason, the Wavelength-Division Multiplexing (WDM) has been recognized as the leading alternative among various optical communication system technologies which have been proposed up to now.
The WDM technology is a wavelength division multiplexing method which binds and sends light having different wavelengths through a single strand of optical fiber. The WDM technology provides a point-to-point dedicated channel for each subscriber through the independent allocation of wavelengths, each of which is inherent to one subscriber, and uses an inherent optical wavelength for each subscriber. Thus, the WDM technology is capable of providing a high speed service.
For example, a WDM-PON (WDM Passive Optical Network) technology has advantages in that since the WDM-PON uses many wavelengths as compared to a TDM (Time-Division Multiplexing)-PON, such as an E-PON (Ethernet-PON) or a G-PON (Gigabit-PON), which is a time division method, a bi-directional symmetric service is assured and bandwidths are independently allocated, and since signals with different wavelengths are received only by corresponding subscribers, security is excellent.
One of the requirements in the WDM-PON is that optical terminal devices are irrelevant to used wavelengths. The inventor(s) has noted that when this is not satisfied, various kinds of optical terminals corresponding to the number of used optical wavelengths are needed. The inventor(s) has noted that in such a case, considerable difficulties are caused in manufacturing, management, and installation of optical terminal devices.
In order to apply bi-directional optical modules in a CWDM method, the inventor(s) has noted that each of the modules applied to transmission and reception uses 9 channels among 18 CWDM channels. The inventor(s) has experienced that the CWDM method halves optical line use efficiency. Accordingly, technologies that use a single channel in upstream (subscriber→central station) and downstream (central station→subscriber) signal transmissions have been proposed. However, the inventor(s) has experienced that use of a single channel causes a link fail between optical communication networks due to reflection and backscattering on an optical line.